Lots of nonsense in this movie

Yeah, I forgot about that. Not only will sound not travel in a near vacuum, but without any air to breath, there would be no air in their lungs to vibrate their vocal cords to produce any sound in the first place.

Yes, Clark got sucker punched from behind at first, but then he got up with a determined look on his face and walked up to Rocky, and still failed to mount any sort of offense or defense.

Keep in mind that when Superman fought his fellow Kryptonians, their attacks hurt him because they were on the same power level as him, yet he continued to fight. The issue isn't that he lost the fight to Rocky, it's that he didn't put up any fight at all.

Man of Steel, Woman of Kleenex by Larry Niven.

"1. There is a short story out there called Man of Steel, Woman of Tissue (or something like that) that addresses the problem. Clark's sperm are also super and potentially deadly to the initial host as they would disperse at superspeed once the available egg was fertilized. His seed would likely find the closest 100 women as the crow flies and that includes the damage done as they take that closest route through flesh."

Only information included in the movie, either explicitly or tacitly, can resolve issues in the movie. Also, that explanation doesn't make sense. If his automatic biological functions were amped up to super levels, then his heartbeat and blood circulation would be very noisy. Imagine a heart beating with millions of times the force of a standard human heart; it would sound like thunder. His normal breathing would cause windy conditions around him. Even blinking his eyes would send gushes of wind and would be loud like when you clap your hands together. Urinating would be like a waterjet cutter, which can cut through steel, let alone a toilet.

"3. I can accept Clark being completely unready for hth combat, even with the weight/size disparity."

Yet he was ready for hand-to-hand combat with his fellow Kryptonians, who, being as strong as him, could, and did, hit him hard enough to hurt him. And those were people with military training.

"4. Not entirely true. I do agree that the distance Supe flew from the attack is extravagant but he would be thrown back and without Ursa flying an equal amount backward. Doesn't quite work that way (in a world where people can fly and if they were in space, perhaps something like what you cite). I worked in a pizza joint decades ago and we would settle arguments by throwing the massive dough bag at each other in the walk-in freezer. It would always send the target flying backward."

When you throw something, it pushes against you with the exact same amount of force that you pushed against it with. If two people are equal, and the person on the receiving end is ready, they won't get sent flying backwards when they catch the bag of dough. In the case of Ursa, she was substantially smaller than Superman, and it follows that she was substantially weaker too.

Imagine Sarah Douglas throwing a bag of dough to Christopher Reeve, who outweighs her by probably 90 pounds and is probably 3 or 4 times as strong. He could obviously catch it without issue. And even if Superman were caught completely off guard, he wouldn't be forced back by any meaningful amount. He has extremely strong muscles to brace himself against the ground, and more importantly, he can propel himself through the air with extreme force (fly at outrageous speeds), and his flying force alone would allow him to way more than counteract the force of that manhole cover. He also has extremely fast reflexes (which is part and parcel of being able to move at extreme speeds), so fast that they would seem instantaneous compared to a human's reflexes.

"High nostalgia value for me though."

Same here. It was the first Superman movie I ever saw. When I was 7 in '82 I watched it on HBO at my neighbor's house quite a few times. I'll always associate that old metallic 3D flying HBO logo with Superman II, since it always played before the movie and it seemed so Superman-esque anyway:

https://youtu.be/M9N9AByVnZ4

I cannot. That part of S1 was among the worst things shown in a movie ever. Top 3 shitty. Worse even than Supe throwing his chest emblem. Outside of a few nuclear level stupid parts, S1 is great, though.

"A Kryptonian may have to give up their powers in order to have sex with a human, or it'd be very dangerous for the human."

Dangerous how?

"Regarding the fight at the diner, IMHO Clark was undone by the fact that being punched actually hurt. He'd been invulnerable before, he didn't know how to fight like a human, which includes taking some punches and keeping on fighting anyway."

I already addressed that in two previous posts:

1. "Keep in mind that when Superman fought his fellow Kryptonians, their attacks hurt him because they were on the same power level as him, yet he continued to fight."

2. "Yet he was ready for hand-to-hand combat with his fellow Kryptonians, who, being as strong as him, could, and did, hit him hard enough to hurt him. And those were people with military training."

"Some comics nerd might be able to explain the Phantom Zone, whether it has a geographical location, or whether it's another dimension that might be accessible from anywhere in time and space, whether people age while they're there."

If it's some other dimension, then a nuclear explosion in our dimension wouldn't have any effect on them. Nuclear explosions don't cross dimensions.

"Regarding the laws of physics: Beings who can fly and hover in mid-air aren't as subject to the laws of action and reaction like we are."

Of course they are.

"If a Kryptonian can hover in mid-air and throw stuff, they don't necessarily have to fly backwards, because they can hold their position in mid-air as solidly as a human standing on the ground."

Exactly, and the Kryptonian that got hit with the thing they threw wouldn't fly backwards either, because he can also hold his position in mid-air just as solidly as the Kryptonian that threw the thing, and that's the problem with the scene.